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1 December 2005Relationships between Habitat Characteristics and Fish Assemblages in Small Streams of Central Amazonia

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Abstract

Small streams with acidic, nutrient-poor waters form a dense hydrological system in Central Amazonia. However, little is known about the fish assemblages that occur in these systems. We investigated the relationships among stream size, substrate, and other physical-chemical factors and fish distributions. Fish assemblages and stream characteristics were sampled in 50-m long sections of streams at 38 sites distributed throughout the 100-km2 florestal reserve. Forty-nine species were encountered. The mean richness was similar among sites; however, community composition was correlated with physical and chemical characteristics of the streams. The mean number of species per site (X̄ = 9) was low in relation to the total number of species recorded from the reserve (49) and in relation to the ichthyofauna that has been recorded from small forest streams near the study area. This contrasts with studies in temperate zones where strong patterns of species addition along the river continuum were found, resulting in prominent species richness gradients. The high between-site turnover in species composition and the strong habitat specificity indicate that it will be necessary to create a network of reserves to efficiently conserve the fish fauna of small forest streams in Central Amazonia.Na Amazônia Central, pequenos riachos de águas ácidas e pobres em nutrientes constituem uma densa rede hidrica. Contudo, pouco é conhecido sobre a riqueza e abundância de sua ictiofauna. Para determinar a composição ictiofaunistica existente, bem como determinar a relação entre o tamanho dos igarapés, substratos presentes nos leitos, e fatores fisico-quimicos e a estrutura da comunidade, nós amostramos trechos de 50-m em 38 locais distribuidos em uma reserva de 100-km2. A riqueza média foi semelhante entre os sitios de amostragem. No entanto, a composição de espécies foi relacionada com caracteristicas fisicas e quimicas dos riachos. O número médio de espécies por local (X̄ = 9) foi pequeno em relação ao número total de espécies encontrado na reserva (49) e em relação à ictiofauna que foi encontrada em pequenos riachos próximos à área de estudo. Isto contrasta com estudos realizados em zonas temperadas, onde um padrão muito forte de adição de espécies ao longo das bacias foi encontrado, resultando em um gradiente acentuado de riqueza de espécies. A alta troca na composição de espécies entre locais, e a alta especificidade de hábitat, indica que seria necessário criar uma rede de reservas para conservar eficientemente a ictiofauna de pequenos riachos na região.